The invention relates to a fuel cell with an anode-cathode stack, which comprises at least one surface layer, which fuel cell is designed with a first channel structure having a multiplicity of first channels for conducting a first fluid in a first direction over the surface layer, which fuel cell is designed with a second channel structure having a multiplicity of second channels for conducting a second fluid in a second direction over the surface layer, wherein the second direction extends in the main transversely to the first direction, which fuel cell is designed with a first feed structure for feeding the first fluid into the multiplicity of first channels, and which fuel cell is designed with a second feed structure for feeding the second fluid into the multiplicity of second channels. The invention also relates to a use of such a fuel cell on a motor vehicle.
Fuel cells of the type according to the invention are designed especially as a polymer electrolyte fuel cell (PEFC), or a proton exchange membrane fuel cell (PEMFC) with an anode-cathode stack (bipolar plate stack) which comprises a multiplicity of active surface layers. The individual surface layer is designed with an anode and a cathode which are separated by a membrane. So that proton transport can take place in the membrane, hydrogen (in the form of gas) and oxygen (in the form of air) and also, if necessary, a coolant (in the form of liquid water) have to be fed into the surface layer as reaction fluids.
To this end, the individual surface layer is designed with a first channel structure for conducting a first fluid over the surface layer and a first feed structure for feeding the first reaction fluid into the first channel structure. Also, provision is made on the surface layer for a second channel structure for conducting the second fluid over the surface layer and a second feed structure for feeding the second fluid into the second channel structure. The individual channel structures are designed in each case with a multiplicity of channels lying next to each other and in this way extend over the entire surface of the surface layer. The feed structures are located on the edges of the surface layer and serve for introducing the respective fluid into the multiplicity of associated channels as uniformly as possible. The feed structures can be integrated as a so-called internal manifold in a plate representing the feed structure. Alternatively, the feed structures can be designed as so-called external manifolds. In the case of this design, the feed structures are connected on the outside to the anode-cathode stack as separate components.
For cost and weight reasons, this type of external manifold is to be preferred. With regard to the sealing of an interface which then results between the external manifold and the anode-cathode stack such designs are not without problems, however. This is especially the case if for feeding the first and second fluids channel structures which extend transversely to each other, so-called cross-flow fields, are to be used. For such structures, it is necessary in particular to arrange manifolds on three to four edges of the surface layers which in this case are rectangular.
Created according to the invention is a fuel cell with an anode-cathode stack, which comprises at least one active surface layer which is designed with a first channel structure having a multiplicity of first channels for conducting a first fluid in a first direction over the surface layer, which fuel cell is designed with a second channel structure having a multiplicity of second channels for conducting a second fluid in a second direction over the surface layer, wherein the second direction extends in the main transversely to the first direction, which fuel cell is designed with a first feed structure for feeding the first fluid into the multiplicity of first channels, and which fuel cell is designed with a second feed structure for feeding the second fluid into the multiplicity of second channels. According to the invention, the first feed structure and the second feed structure are both arranged on a first edge of the surface layer and the first feed structure additionally has an edge channel for feeding the first fluid to a second edge of the surface layer which is oriented transversely to the first edge.
With the design according to the invention, it is possible to realize a cross-flow field which manages with only two external manifolds. The costs and complexity of the solution according to the invention are comparatively correspondingly low.
To this end, according to the invention both fluids are fed on one edge of the respective surface layer and then one of the fluids is conducted by means of an edge channel, transversely to this first edge, along a second edge of the surface layer. This type of lateral diversion of the first fluid to a second edge of the surface layer according to the invention is preferably carried out with the hydrogen reaction gas. Hydrogen has a low viscosity so that a diversion is possible even in a small installation space. In this case, an installation space, provided anyway on the surface layer, beneath a seal can be used for the edge channel. Also, a saving can be made on installation space for otherwise necessary manifolds on the other edges of the stack. The overall volume of the anode-cathode stack according to the invention can therefore turn out to be smaller than in the case of conventional stacks. Furthermore, the aforesaid sealing problems are particularly small in the case of the solution according to the invention.
In an advantageous embodiment of such a fuel cell according to the invention, the surface layer is of rectangular design, wherein the first edge is then a first longitudinal side of this rectangular shape and the second edge is a second longitudinal side of the rectangular shape which is adjacent to the first longitudinal side.
The edge channel for feeding the first fluid preferably extends along the entire second edge of the surface layer. With an edge channel of such length, the first fluid can be diverted across the entire second edge into channels of an associated channel structure which begin there.
In this case, a further edge channel is then also formed, preferably on a third edge of the surface layer opposite the second edge, for discharging the first fluid from the multiplicity of first channels along the entire third edge of the surface layer. In this way, a Z-shape is formed, in which the first fluid is fed on one side of the anode-cathode stack, then conducted through the stack transversely to the previous direction, and then in turn discharged on the other side transversely to the previous direction.
Alternatively, the edge channel for feeding the first fluid extends along only a part of the second edge, the first channels are designed in the associated surface layer in an S-shaped extending manner, and on a third edge of the surface layer opposite the second edge a further edge channel for discharging the first fluid from the multiplicity of first channels extends along only a part of the entire third edge. With this constructional form, the available installation space can be utilized in a particularly efficient way.
The second feed structure, in the case of the fuel cell according to the invention, is preferably designed with a second feed channel, extending perpendicularly to the surface layer, for feeding the second fluid and is arranged on the first edge in its corner region facing away from the second edge. In this case, the second fluid, which is preferably air, is conducted across the surface layer especially obliquely to the first and second directions or in an S-shaped manner. In the case of the S-shaped channel routing, the second fluid is first of all conducted in the first direction, then in the second direction and then again in the first direction over the surface layer.
The first feed structure is preferably designed with a first feed channel, extending perpendicularly to the surface layer, for feeding the first fluid and is arranged on the first edge in its corner region to the second edge. The feed and discharge of the first fluid are therefore preferably arranged on two diametrically opposite corners of the anode-cathode stack, which are then located especially laterally next to a central feed or discharge of a third fluid on the first edge, as is explained in more detail below.
Furthermore, provision is preferably made on the fuel cell according to the invention for a third channel structure which is designed with a multiplicity of third channels for conducting a third fluid in a third direction over the surface layer and with a third feed structure for feeding the third fluid into the multiplicity of third channels. In this case, the third feed structure is also arranged on the first edge. With such a third channel structure, the third fluid, which is preferably a coolant, can be conducted especially obliquely to the first and second directions or in an S-shaped manner across the surface layer. In the case of the S-shaped channel routing, the third fluid is first of all conducted in the first direction, then in the second direction, and then again in the first direction across the surface layer.
In this case, the third feed structure is preferably designed with a third feed channel, extending perpendicularly to the surface layer, for feeding the third fluid and is arranged on the first edge in its middle region. The third feed channel is located on the third edge, that is to say especially between the first and the second feed channels. A central, middle feed of the third fluid into the third channels, which in this case extend especially in parallel next to each other across the surface layer, is possible in this way.
The invention is finally also specifically directed towards the use of such a fuel cell according to the invention on a motor vehicle, especially a hybrid vehicle.
Exemplary embodiments of the solution according to the invention are explained in more detail below with reference to the attached schematic drawings. In the drawing:
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.